The present invention concerns shutter-diaphragm systems provided with light-totalizing circuitry. In such systems, during the course of the exposure itself, the exposure aperture of the camera progressively increases in size, and a scene-light-dependent timing circuit generates a totalized-light signal which upon reaching a predetermined value causes a terminate-exposure signal to be generated, followed by blocking of the exposure aperture. In such systems, the totalized-light signal should vary not only in dependence upon the scene-light level per se, but furthermore in dependence upon the progressive size increase of the exposure aperture occurring during the course of the exposure.